In the case that a hydraulically operated variable valve actuation mechanism is provided in a timing sprocket, a timing pulley or the like of an internal combustion engine, a hydraulic oil supply and drain oil passage connecting an oil control valve with the variable valve actuation mechanism is generally provided so as to pass through a camshaft. In this case, there has been proposed a structure in which the oil control valve is installed to the cylinder head cover, and the hydraulic oil is supplied and drained via the oil passage within the cam cap and the camshaft by the oil control valve (for example, refer to patent document 1).
In order to install the oil control valve to the cylinder head cover, it is necessary to form an installation hole in the cylinder head cover. For example, in the case that the installation hole is bored in the cylinder head cover cast from a metal, there is a risk that a cast defect in an inner portion of the cylinder head cover is exposed to a surface defining the installation hole. If the cast defect is exposed to the surface defining the installation hole, an oil tightness between the oil control valve inserted to the installation hole and the surface defining the installation hole is lowered, and a problem is generated in a hydraulic control.
The problem mentioned above may be generated in the same manner in the case that the cylinder head cover is formed of a resin. In the case of the resin cylinder head cover, the oil tightness between the surface defining the installation hole and the oil control valve is further lowered due to a poorness of a dimensional accuracy of the installation hole, a difference of thermal expansion rate between the oil control valve and the cylinder head cover, a creep phenomenon or the like.
Patent Document 1: Japanese Patent Publication No. 3525709